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Subject: Re: [PATCH v2] x86/xen: don't unbind uninitialized lock_kicker_irq
To:     =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= <jgross@suse.com>,
        Brian Masney <bmasney@redhat.com>, sstabellini@kernel.org
Cc:     tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org,
        hpa@zytor.com, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org, dustymabe@redhat.com
References: <20201107011119.631442-1-bmasney@redhat.com>
 <5950df5c-79d6-b2bc-4f2b-35624a3c0d1e@suse.com>
From:   boris.ostrovsky@oracle.com
Organization: Oracle Corporation
Message-ID: <87d1122a-ca5a-786b-5b25-4caaaeaf386a@oracle.com>
Date:   Mon, 9 Nov 2020 16:59:14 -0500
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On 11/9/20 12:34 AM, Jürgen Groß wrote:
> On 07.11.20 02:11, Brian Masney wrote:
>> When booting a hyperthreaded system with the kernel parameter
>> 'mitigations=auto,nosmt', the following warning occurs:
>>
>>      WARNING: CPU: 0 PID: 1 at drivers/xen/events/events_base.c:1112 unbind_from_irqhandler+0x4e/0x60
>>      ...
>>      Hardware name: Xen HVM domU, BIOS 4.2.amazon 08/24/2006
>>      ...
>>      Call Trace:
>>       xen_uninit_lock_cpu+0x28/0x62
>>       xen_hvm_cpu_die+0x21/0x30
>>       takedown_cpu+0x9c/0xe0
>>       ? trace_suspend_resume+0x60/0x60
>>       cpuhp_invoke_callback+0x9a/0x530
>>       _cpu_up+0x11a/0x130
>>       cpu_up+0x7e/0xc0
>>       bringup_nonboot_cpus+0x48/0x50
>>       smp_init+0x26/0x79
>>       kernel_init_freeable+0xea/0x229
>>       ? rest_init+0xaa/0xaa
>>       kernel_init+0xa/0x106
>>       ret_from_fork+0x35/0x40
>>
>> The secondary CPUs are not activated with the nosmt mitigations and only
>> the primary thread on each CPU core is used. In this situation,
>> xen_hvm_smp_prepare_cpus(), and more importantly xen_init_lock_cpu(), is
>> not called, so the lock_kicker_irq is not initialized for the secondary
>> CPUs. Let's fix this by exiting early in xen_uninit_lock_cpu() if the
>> irq is not set to avoid the warning from above for each secondary CPU.
>>
>> Signed-off-by: Brian Masney <bmasney@redhat.com>
>
> Reviewed-by: Juergen Gross <jgross@suse.com>


Applied to for-linus-5.10b.


-boris